Here's the problem: they're only decent in what is effectively melee range. Getting close to big bads is a good way to get killed. What about encounters where you're forced into point blank range? There the looooong reload is what kills me. I can't think of a single situation where I'd use a shotgun over a fusion rifle which is still effective at longer ranges, or just use my melee in PvE. Even when they double the damage, all those things will still be true.